embryology Flashcards
what weeks are the embryonic period
3-8
what weeks are the foetal period
9-40
what weeks are the first trimester
weeks 0-12
what weeks are the second trimester
weeks 12-24
what weeks are the third trimester
24- birth
name the phases of embryogenesis
gametogenesis
fertilisation
cleavage
gastrulation
formation of body plan
organogenesis
what takes place during gametogenesis
formation of haploid gametes
oogenesis
spermatogenesis
how many pairs of chromosomes are in a gamete
23
describe oogenesis
formation of the female gametes
starts at development and ends at menopause
weeks 28-30 of development oocytes begin meiosis but arrest in prophase until puberty
when is reproductive lifespan of the female determined
during foetal life
describe spermatogenesis
formation of the male gametes
takes place during puberty and continues throughout life
how many sperm are produced each day
~65 million per gram of testicular tissue
decreases with age
what is aneuploidy
abnormal number of chromosomes
describe fertilisation
fusion of gametes to form a zygote
define zygote
diploid single cell embryo
where does fertilisation usually occur
ampulla
what is polyspermy
when multiple sperm fertilise one egg
leads to a non-viable embryo
describe cleavage
rapid mitotic cell division
cells decrease in size so no change in the size of the zygote
formation of morula (16+ cells) then blastocyst (~4 days after fertilisation)
cavity inside blastocyst - trochoblast will form placenta and epiblast will form embryo
describe gastrulation
formation of the germ layers - takes place in week 3
ectoderm, mesoderm and endoderm form
body axis established
what does the ectoderm go on to become
outer layer of the embryo
skin and nervous tissue
what does the endoderm go on to become
inner layer of the embryo
GI and respiratory tracts
what does the mesoderm go on to become
middle layer of the embryo
muscle and skeletal tissue
what is embryonic folding
formation of the body plan
what is organogenesis
formation of the organs and organ systems
basis of this is in place by the end of the embryonic period, continues to develop during the foetal period
when does the foetus growing in length mainly occur
2nd trimester
when does increase in foetal weight mainly occur
3rd trimester
what occurs during the foetal period
tissues mature and become functional
overt sexual differentiation
bone laid down
connections made in CNS
2nd trimester - grow in length
3rd trimester - weight gain
what is the term used instead of superior when referring to an embryo/ foetus
cranial
what is the term used instead of inferior when referring to an embryo/ foetus
caudal
what is the term used instead of anterior when referring to an embryo/ foetus
ventral
what is the term used instead of posterior when referring to an embryo/ foetus
dorsal
what factors control development of an embryo/ foetus
gene expression
epigenetic factors - preferential expression of genetic factors in relation to the environment
